Field of the Invention
The present invention relates to a method and device for manufacturing a fiber-reinforced plastic structure.
Description of the Related Art
Being lightweight and excellent in mechanical strength, fiber-reinforced plastics (FRPs) are used for structural members of an aircraft and the like.
For example, a skin of an aircraft and multiple stringers reinforcing the skin are also formed of FRPs. The multiple stringers are provided at intervals on the back surface of the skin.
Here, as shown in Mitsubishi Heavy Industries Technical Review, Vol. 42, No. 5 (December 2005), “Research in the Application of the VaRTM Technique to the Fabrication of Primary Aircraft Composite Structures”, co-bond molding is practiced in which a fiber base material as the FRP material of the stringer is disposed on a pre-molded skin, and a resin impregnating the fiber base material is heated to cure. When the resin has cured to a predetermined hardness, the stringer is molded, and at the same time the stringer is integrally bonded to the skin through an adhesive. Thus, a fiber-reinforced plastic structure is manufactured.
In the co-bond molding of the skin and the stringer, the FRP material of the stringer disposed on the skin is pressed by a mandrel which is positioned relative to the mold supporting the skin. The skin and the mandrel are then sealed between a bag film and the mold to create an enclosed space, and the stringer is molded while the enclosed space is being depressurized by evacuation of the air.
In order to position the stringers at predetermined positions on the skin, a positioning jig is engaged with upper parts of mandrels arranged on the skin. This positioning jig is extremely expensive, as it is produced laboriously by cutting a metal block with a five-axis machining tool into a shape that fits the upper parts of the mandrels disposed on the skin's curved surface.
On the other hand, as shown in FIG. 10, a positioning jig 8 which spans a mold 5 in the width direction and engages with the upper parts of mandrels 7 is also used. This positioning jig 8 includes a frame 81 supported by the mold 5 at its both ends, and blocks 82 respectively clamping the mandrels 7, and positions the mandrels 7 in the direction of arrangement of the mandrels 7.
The positioning jig 8 requires no cutting work, since it can align the blocks 82 with the upper parts of the mandrels 7 by a spring (not shown). Nevertheless, the positioning jig 8 is expensive as it includes many components such as the multiple blocks 82 and the spring provided for each block 82.
In addition, even when the mandrels are positioned by the positioning jig 8 or the positioning jig produced by cutting work, the positioning jig undergoes thermal expansion when the FRP material is heated to cure, which can degrade the positional accuracy of the stringer. Once the stringer shifts from the determined position, it is difficult to fit the stringer with its mating part.
To avoid this problem, the positioning jig can be formed from Invar, which has a low thermal expansion coefficient as with the FRP; however, the frame 81 and the block 82 of the positioning jig 8, or the positioning jig produced by cutting work have a massive form, which would require a large amount of Invar to be used and drive up the cost of the jig.
While the positioning jig can also be formed from an FRP, molding the FRP so as to fit the skin's curved surface requires complicated work, making the jig no less expensive than the jig produced by five-axis cutting work.
Moreover, with the conventional positioning jig, which presses the mandrels over a bag film, the bag film can be damaged due to rubbing between the positioning jig and the mandrels, etc. If the bag film is damaged, the resin and the fiber base material fail to be sufficiently densified, which affects the quality of the molded stringer.
Therefore, the present invention aims to provide a device and method for manufacturing a fiber-reinforced plastic structure which can position a long fiber-reinforced plastic member at a predetermined position relative to a plate-like fiber-reinforced plastic member, while reducing the cost of the positioning jig and securing the quality.